Process for making conductive-core magnetic device



June 15,1965

E- T. K- CHOW ETAL PROCESS FOR MAKING CONDUCTIVE-CORE MAGNETIC DEVICEFiled' May 19, 1960 2 u. .1; t 91:: 3: 5: f 't. I I c! in; 'gg u; 5 55:1 20 k0 PROCEDURE OUTLINE I 1. Clean wire with alkaline cleaner.

2. Rinse with distilled water.

3 Remove thin surface layer with conc. HNO sat. 4 Rinse with distilledwater.

5- Electroplate on iron-nickel thin layer. 6. Rinse with distilledwater. 7. Dry with acetone.

6. Apply protective urethane resin coat.

INVENTORS Eric T.K. Chow Harry L. Watkins ATTORNEYS United I StatesPatent 3,189,532 PROCESS FOR MAKING CONDUCTIVE CORE' MAGNETIC DEVICEEric T. K. .Chow and HarryL. Watkins, Califl, assignors to The NationalCashRegister Company, Dayton, Ohio, a corporation of Maryland I FiledMay 19, 1960,'Ser. No. 30,362

3 Claims. ((1204-28) The present invention is in the field of magneticdevices used, for example, as logical elements and/or informationstoredevices in information-processing systems such as digital computers.More particularly, the invention relates to an improved process ofproducing slender rod-like bistable magnetic devices having as a core asmall gauge stiti resilient non-magnetic electric conductor with anbistable. magnetic devices having as a core a small-gauge herent thinelectroplated layer of iron-nickel composition, and the improved productproduced by the process.

As indicated foriexample, incopending application Serial No. 791,695, ofTsu, and in copending application Serial No. 827,412, now US. Patent No.2,94s,2 17 of Fisher et al., prior investigations have proven the meritsof fine-gauge rod-like bistable magnetic devices having orientedmagnetic films, employed as binary informationstore or memory elementsand as logical elements in computer systems. A first type of device ofthis nature comprises a resilient base of an electrically non-conductivematerial such as glass, with an oriented thin film of adherentbistable'magnetic materiaL' A second type of such device comprises aresilient base formed of electrically conductive material such as acopper alloy wire and an electrolytically applied layer or film ofbistable magnetic material which in the finished devices has been soapplied or so disposed that there is an easy direction of magnetizationwhich is oriented at an angle to the longitudinal axis of the device.Orientation of the direction of easiest magnetization may be attainedeither by deposition of the magnetic material under the influence of aproperly oriented magnetic field (as in Fisher et al., supra), or, insome cases, by mechanical operations such as by mechanically twistingthe base wire before or after applicat on of the magnetic material, orby scratching or grooving the wire to provide spirally orienteddeformations or alterations of the surface of the wire (as in Tsu,supra), and

which deformations cause the magnetic material to have a similarlyoriented'easy direction of magnetization. The orientation of themagnetization characteristic of the material as just briefiy describedis for the purposeof permitting reversal of the direction of themagnetization, that is, reversal of the remanent state of the bistablemagnetic material, by a current in one direction or the other throughthe conductive core or'base concurrently aided by one or more currentspassed through coils encircling the rod-like device. In general it hasnot been contemplated that this second'type or class of magnetic deviceswould be useful in the absence of the spiral orientation of the magneticaxis of the magnetic material. I i

It is to a typeof device somewhat similar to the men- Los Angeles,

in respect to different devices produced in ditferent v batches orproduction lots.

Briefly, in accordance with the invention a stiff resilient wire orfine-gauge rod of copper-beryllium alloy is thoroughly cleaned andrinsed in or with distilled water in accord with a special procedure,and is immediately electroplated in a special electrolytic bath toproduce a thin film of bistable magnetic material comprising a highpercentage' of iron and a minor proportion of nickel on the peripheralsurface of the wire or fine-gauge rod, along the length thereof. Thepreferred composition of magnetic material is about 97% to 98% iron and3% to 2% nickel, by weight, although acceptable devices may be producedwith the composition ranging from about 93% to 99% iron and theremainder nickel. In general the switching time (time for reversal ofstable state) of the material is shortened as the percentage of nickelin the composition is decreased. While the magnetic materialmay be andpreferably is electroplated onto the wire while the latter I is disposedin a magnetic field so directed relative to the wire that the magneticmaterial is oriented along the Wire similar tovv that disclosed incopending application for US.

patent, Serial No. 802,494, now abandoned, filed March 27, 1959, byRichard M. Clinehens and Donal A. Meier; or the electrolyte may be thathereinafter specifically described.

Previous efforts to prepare bistable magnetic rod-like devices of thegeneral type forming the subject of the present invention met withindifferent and extremely variable results. The magnetic characteristicsof the material, such as the coercivity and rectangularity" of themagnetization or hysteresis characteristic curve, varied considerablyalong the length of the wire or rod-like device. Since the devicesareintended to be used as long lengths and in large numbers in magneticdata-store matrices, rather than as very short individual portions, it

is extremely desirable that the magnetic characteristics be as uniformas possible throughout'the entire length of each rod-like device andfrom device to device among a large number of the devices. Prior to thepresent invention, no reasonable or acceptable degree of uniformity ofthe magnetic characteristics could be attained when electricallyconductive wires or rod-like cores were used. The previously acceptablerod-like bistable magnetic devices of the general character of thoseprovided by the present invention were ofa type using a slender glass(non-conductor) filament as a base structure for supporting the magneticmaterial. The devices using glass filament as a base, are, however,relatively expensive because of the high cost of uniform filaments anddue to the relatively complicated procedurere quired to produceacceptable and uniform magnetic devices. The stiff resilientcopper-beryllium wire base usedaccording to the present invention isrelatively inexpensive and, when prepared and electroplated according tothe invention, provides long lengths, of. magnetic 'rod-likex bistable'dc.-

Patented Jime 15, 1965 vices possessing exceptionally superior magneticcharac-' teristics and of excellent uniformity. Further, the processsteps required in production of the devices are by the invention greatlysimplified and reduced in number, thus both improving the device fromthe engineering standpoint and considerably reducing the cost per unitlength of the devices.

From the preceding general description of the nature of the invention itis evident that a principal object of the invention is to provide animproved bistable magnetic rodlike device having a resilient rod-likeelectrically conductive base supporting a magnetic film or plate ofexcellent magnetic characteristics and improved uniformity, the magneticmaterial having either no easiest direction of magnetization(unoriented), or oriented to have an easiest direction of magnetizationlongitudinally of the conductive base. Another object is to provide asimpler and less expensive process for production of slender rodlikedevices having a thin film or layer of bistable magnetic materialsupported by a stiff resilient electrically conductive rod-like (wire)base.

Another object is to provide a stiff, resilient, very slender rod-likemagnetic device having a surface layer of bistable magnetic material ofuniform characteristics and which device is not brittle.

Another object of the present invention is to provide improvements inslender rod-like magnetic devices suit able for use as core-stock orcores for magnetic information-store or magnetic switch devices.

Other objects and advantages of the invention will become evident ormade so in connection with the appended claims and the followingexplanation of the process and description of.the product comprised intheinvention. The product is illustrated in the drawings, in which:

FIG. 1 is a view, greatly magnified, of a magnetic device comprisingastiff resilient conductive core and a thin adherent layer of magneticmaterial possessing a substantially rectangular magnetic hysteresischaracteristic as plotted on Cartesian coordinates, the proportionsbeing distorted to facilitate illustration and an intermediate portionof the device having been broken away;

FIG. 2 is a partly diagrammatic and grossly enlarged view depicting alength of a magnetic device such as is illustrated in FIG. 1, withexemplary windings units comprising plural-turns coils, encirclingrespective assigned portions of the device, with one of the windingsunits shown in the section and with an intermediate portion of thedevice broken out to facilitate illustration;

FIG. 3 is a procedure table outlining the major procedural steps of theprocess of producing the device depicted in FIG. 1.

Referring first to FIG. I, the stiffresilient rod-like magnetic deviceis denoted generally by the ordinal 10, and comprises essentially astiff resilient or spring-like filament or wire 20 of an alloy of copperand beryllium, and a very thin adherent film or coating 30 of magneticmaterial. The rod-like alloy filament or wire. 20, may be of the typewhich has been heat-treated to give it stiffness and resilience. Themagnetic material, which is electrolytically deposited on the wire inaccord with a procedure and by means hereinafter described, i com posedessentially of a large major proportion of iron and a small minorproportion of nickel, and is such asv to possess a substantiallyrectangular magnetization hysteresis characteristic curve. The preferredproportions of iron to nickel are of the order of 97 parts iron to 3parts nickel, by weight; however, usable devices are producible with thepercentage of iron in the range from 93 to 99 and the percentage ofnickel in the range from 7 to 1, all by weight. The relative percentagesof iron and nickel may be varied by variation of the proportion of ironand nickel salts in the electrolyte bath in which the magnetic materialis electro-plated onto the rod-like base. The copper-beryllium rod orwire base is of fine gauge, that is, of the order of from five to fiftymils in maximum 4 cross-sectional dimension (diameter, in the case of awire circular cross-section); and a preferred examplary form is a veryspringy straight wire of twelve mils diameter. A preferred exemplarymagnetic film or layer is one of 97 parts iron and 3 parts nickel byweight, of the order of 3000 angstroms thick (as computed by indirectmeth- ,ods), and is possessed of a very rectangular hysteresischaracteristic curve as plotted in Cartesian coordinates, and ispreferably unoriented. While the rod-like base member may be as small asfive mils or as large as fifty mils in diameter in special cases, andthe magnetic coating as thick as 10000 angstroms or as thin as 500angstroms for certain special applications, the above given preferreddimensions have been found to provide devices having sufficient strengthand rigidity to permit handling without necessity for exercise ofunusual care, and having excellent magnetic characteristics for use indata-store arrays and matrices.

In use in an information-store apparatus, a suitably long length of thecoated rod-like device is used in conjunction with a series ofspaced-apart coil units, such ascoil units 40 illustrated in FIG. 2 ofthe drawings. The coil units 40 are there shown disposed on a magneticdevice 10 which comprises a stiff resilient copperberyllium wire base20' and an adherent thin layer or film of bistable magnetic material.Each coil unit comprises a plurality of plural-turns single-layersolenoidcoils arranged in generally concentric relationship andencircling a respective small length or portion of the magnetic thinfilm 30. An exemplary coil unit as shown comprises three superposedcoils such as 40a, 40b, and 400, each of ten turns of conductor, andeach having a respective pair of coil leads such as 40a'-40a, 40b- 40b",and 406-400". The conductors are insulated, and

' may be in the form of fiat wires, stranded wires, parallellaid fiatwires, or other suitable forms. The coil units are in use spaced alongthe magnetic rod-like device 10 sufficiently far apart to obviateundesirable mutual magnetic interactions; and this spacing mayalternatively be effected by winding the coil units on the rod-likemagnetic device or, and preferably, by the coil units being disposed inarrays or matrices in coaxial relationship along bores in an embedment(not shown). In the latter arrangement coil units are relatively fixedin coaxial disposition with respect to each other by the embeddingcompound and they and bores coaxial with the coil units and extendingthrough the embedding material are of internal diameter suitable foreasy insetrion of the magnetic rodlike devices into the bores and thrughthe coil units. As many coil units as may be desired are arranged ordisposed in spaced-apart relationship along a magnetic rod-like device,in either of the described modes; and for example, the number of coilunits arranged for cooperation with respective portions of a magneticrod-like device may be forty, or more, or less. Each coil unit thuscooperates with its own respective portion of the long magnetic film.Examplary ten-turn coils may be of the order of one sixteenth of an inchin length. The general nature of the bistable magnetic film, the coilsof the units, and the interactions therebetween are like or similar tothose described and explained in copending application of Donal A.Meier, Serial No. 728,739, filed April 15, 1958, now abandoned, to whichreference may be had forfurther details in respect to these matters. Thepresent invention provides and presents improvements over the'proceduresand devices disclosed in the aid application Serial No.'728,739.

With reference to FIG.'3, the preferred electrolyte plating bath andprocedure for producing the improved device will next be disclosed andexplained. Prior to being subjected to electroplating action in theelectrolytic bath, the copper-beryllium alloy wire is subjected to athorough cleaning in a suitable alkaline cleaning bath (step 1). As anexample, a solution of the commercially available product named ShipleysAlkaline Cleaner I (step 2).

isf'found to give excellent results. Immediately follow: ing thealkaline" bath treatment, the copper-beryllium base rod or wire isthoroughly rinsed with distilled water thinsurface layer of the,copper-beryllium alloy (step 3);

and the acid treatment is immediately followed by a tion made up from290 grams of FcCl -4H O, 12 grams of NiCI -6H O and 238 grams of CaClper liter of solution, with addition of dilute l-lCl. if necessary, tobring the pH to a value of 1001005. Enough iron powder or iron wool tomake certain that the solution is ferrous rather than ferric may beadded to the electrolyte bath. An acceptable procedure for effecting theelectroplating is to progressively pass or draw the wire or rod"downwardly through a three-inch long zone of contact with theelectrolyte at a speed of about five inches per minute, using a platingcurrent of from 12 to 25 milliamperes, at room temperature. Care shouldbe exercised to apply the plating current uniformly over the exposedlength and periphery of the base or wire; and this may be effectivelyaccomplished by employing a tubular or spiral anode electrode throughand along the axis of which the wire is traversed or'drawn. The wire isconnected to the current source as the cathode of the system. Theexposure time and current density may be varied somewhat, depending uponthe thickness of plating desired, and the size of wire. The precedingdata relate to plating of an exemplary copper-beryllium wire of ten milsdiameter. Analysis of the plating deposited on the exemplary wireindicates a content of approximately 97% iron and 3% nickel by weight,with permissible variation of +-3% in the iron content. It may be notedthat if more rapid switching of the produced magnetic devices isdesired, the switching time may be lowered by using a somewhat lowerconcentration of NiCl -tSH O in the electrolyte; for example, 8 to 10grams per liter of solution. Using concentrations of the order of thatjust noted, switching times faster than 25 millimicroseconds areattainable.

Immediately following electroplating, the plated wire is thoroughlyrinsed with water (step 6) and immediately dried as by means of anacetone bath or spray (step 7); and the dried device is then immediatelygiven a protective coating to avoid oxidation or other degradation ofthe iron-nickel magnetic film or coat. The protective coating may beapplied by dipping the dried device in a suitable moisture proofself-curing resin; and satisfactory protection has been secured using acommercially available resin. As soon as the resin or other protectivecoating has cured or dried, the magnetic device is ready for associationwith coil units as a data-store unit element.

While previous efforts to produce a bistable magnetic coating ofunstressed and/or unoriented magnetic material on a stiff resilient wirehave failed to provide devices The wire is then immersed in aconcentrated nitric acid solution for aperiod sufficient to remove ahaving acceptably uniform magnetic characteristics along long lengths ofthe wire and have failed to produce magnetic rod-like. devices capableof providing as high output voltage and as large signal-to-noise ratioas characterize the now well known glass-filament type of rod-' likemagnetic thin-film device, the procedure of the present inventionprovides long lengths of resilient conductivebase bistablemagneticrod-likedevices of eminently uni-.

form magnetic characteristics not only along the length of any such longdevice but from device to device of. a batch thereof, and from'batch tobath, and also produces devices having as high output potentials andequally good signal-to-noise ratios as characterize the glass-filamenttype of device when both are tested under identical conditions with thesame apparatus. The simplification in the gen-excluding protecting filmover the deposited. magnetic.

procedure of producing the deyice's'i's of greate merit, eliminating"among other things'the steps of applying a thin-film silver substratelayer as a base for the magnetic material and the difficulties attendingthat operation. Furher by permitting the successful production ofuniformly-alike magnetic devices with a base material much cheaper thanthe previously used glass filament base material, a considerable costsaving is effected in the production of bistable magnetic devices of thetype under consideration. Since the rod-like devices are of the order offrom about ten mils to as much as fifty mils in diameter (preferablyabout fifteen mils forthe usual informationstore or memory applications)it is seen that they also possess equally with the better-knownglass-filament rod-' like magnetic devices the distinct and meritoriousadvan-' tages over toroidal and slotted tubular magnetic devices of muchsimpler winding, much greater packin'g'density (bits per unit of spacein a memory device), much smaller driving energy and much fasteroperation. When the relatively higher cost and complicated andpainstaking process of producing the similar glass-rod type of device isconsidered, the considerable advantages of the process and device of thepresent invention become apparent.

While the procedure and the resulting product of theinvention have beendisclosed in detail it is evident from the disclosure that some latitudein specific details is permissible, and accordingly it is desired thatthe scope of a the invention be restricted. only in accord with thedefinition of the invention as portrayed in the appended claims.

What is claimed is: 1. A process of producing a slender 'od-likebistable magnetic device'having a thin iron-nickel film-likecoatingexhibiting a uniform substantially rectangular magnetichysteresis characteristic throughout a long length of the device, saidprocess consisting essentially of: providing a long length of a stiffresilient copper-beryllium wire having a diameter of the order of 5 tomils to serve as the core of said magnetic device, cleaning saidcopper-beryllium wire in an alkaline cleaning solution, immediatelyrinsing the cleaned wire with distilled water,

then immersing the wire in a nitric acid bath for a period each portionof the wire in the plating bath being chosen so as to produce on thewire an adherent uniform bistable magnetic layer having a thicknessranging from 500 to 10,000 angstroms and composed of from about 93% toabout 99% iron and from about 7% to about 1% nickel over the surface ofa long length of the wire.

2. A process according to claim 1, including thestep of providing alongitudinally oriented magnetic field in which the electroplating isaccomplished, whereby to produce a corresponding orientation of an easydirection of magnetization of the magnetic plated onto the wire core. 3.A process according to claim 1, including the steps of providing alongitudinally oriented magnetic field in the region in whichtheelectroplating is effected whereby to produce a longitudinally orientedmagnetic layer, washing anddrying the resulting product, and applying anoxylayer,

References Cited by the Examiner UNtrED STATES PATENTS. J 1,791,642 2/31Schulte 20'443 1,965,399 7/34 Wehe 2041.5 2,507,400 5/50 De Marinis 204-43 .(Otherreferences on following page) UNITED STATES PATENTS OTHERREFERENCES Znpponi 204-43 Naw Advances in Printed Circuits, US. Dept. oSukaccv 29-1S5.5 Commercc Publication 192, Nov. 22, 1948, pp. 25 and 2Beach et a1 20432 relicd on.

Austen 29--155.5 5

A t 34() 174 WINSTON A. DOUGLAS, Primary Examiner. Robinson 204-15Fisher at a! 340 174 figk g ng lf ggg ns, JOSEPH REBOLD, 10m Mitchell.

Eggenberger ct a1 20443 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,189,532 June 15, 1965 Eric T. K. Chow et 211.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 15, for "small gauge-" read small-gauge line 17, strikeout "bistable magnetic devices having as a core a small-gauge"; line 18,for "herent" read adherent line 27, for "this" read that line 64, for"iron-neckel" read ironnickel column 4, line 2, for "examplary" readexemplary line 48, for "insetrion" "read insertion line 49, for "thrugh"read through column 5, line 71, for "bath" read batch column 6, line 1,for "greate" read great line 5, forj'Furher" read Further Signed andsealed this 7th day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A PROCESS OF PRODUCING A SLENDER ROD-LIKE BISTABLE MAGNETIC DEVEICEHAVING A THIN IRON-NICKEL FILM-LIKE COATING EXHIBITING A UNIFROMSUBSTANTIALLY RECTANGULAR MAGNETIC HYSTERESIS CHARACTERISTIC THROUGHOUTA LONG LENGTH OF THE DEVICE, SAID PROCESS CONSISTING ESSENTIALLY OF:PROVIDING A LONG LENGTH OF A STIFF RESILIENT COPPER-BERYLLIUM WIREHAVING A DIAMETER OF THE ORDER OF 5 TO 50 MILS TO SERVE AS THE CORE OFSAID MAGNETIC DEVICE, CLEANING SAID COPPER-BERYLLLIUM WIRE IN ANALKALINE CLEANING SOLUTION, IMMEDIATELY RINSING THE CLEANED WIRE WITHDISTILLED WATER, THEN IMMERSING THE WIRE IN A NITRIC ACID BATH FOR APERIOD OF TIME SUFFICIENT TO ETCH ONLY A SUBSTANTIALLY COMPLETE SURFACELAYER OF THE WIRE, IMMEDIATELY RINSING THE ETCHED WIRE WITH DISTILLEDWATER, AND THEN PRIOR TO APPRICIABLE CHEMICAL DEGRADATION OF THE WIRESURFACE, ELECTROPLATING THE WIRE IN A NICKEL CHLORIDE-IRON CHLORIDEAQUEOUS SOLUTION HAVING A PH OF THE ORDER OF 1.00$0.05 BY CONNECTING THEWIRE AS THE CATHODE OF THE SYSTEM AND PASSING THE WIRE THROUGH A SPIRALANODE ELECTRODE ALONG THE AXIS OF THE WIRE, THE PLATING CURRENT AND THETIME OF EXPOSURE OF EACH PORTION OF THE WIRE IN THE PLATING BATH BEINGCHOSEN SO AS TO PRODUCE ON THE WIRE AN ADHERENT UNIFORM BISTABLEMAGNETIC LAYER HAVING A THICKNESS RANGING FROM 500 TO 10,000 ANGSTROMSAND COMPOSED OF FROM ABOUT 93% TO ABOUT 99% IRON AND FROM ABOUT 7% TOABOUT 1% NICKEL OVER THE SURFACE OF A LONG LENGTH OF THE WIRE.